The cells involved in antibody-mediated suppression of tumor growth will be identified, and the interaction of antibody with these cells in the immune system as well as with tumor cells will be studied. In addition, various cell types isolated from normal, immune and immunologically enhanced animals will be compared in their capacity to suppress tumor growth and in their capacity to help other cells to become immune effector cells. Alloantisera containing antibodies which can suppress tumor growth or cause immunologic enhancement of tumor growth will be fractionated in an attempt to characterize these antibodies.